This invention relates generally to injection molding and more particularly to a method of making an injection molding nozzle with an improved terminal for the integral electric heating element.
Integral electric heating elements have a small diameter resistance wire which connects to a larger diameter conductor to provide a terminal to which the external electrical lead is connected. While the resistance wire of the heating element is electrically connected to the terminal, it must be electrically insulated from the nozzle along its length to avoid grounding. This must be accomplished while providing the terminal with sufficient structural strength to withstand failure due to torquing when the lead wire is connected or disconnected.
Injection molding nozzles having integral heating elements are well known in the art. The applicant's U.S. Pat. No. 4,768,283 discloses a method which provides a protective nickel coating over the heating element which is integrally embedded in a spiral channel. The Canadian patent application Ser. No. 549,517 entitled "Method of Manufacture of Injection Molding Nozzle having Grounded Heating Element Brazed into Pointed Tip", filed Oct. 16, 1987 by Jobst Ulrich Gellert and U.S. Pat. No. 4,768,945 to Schmidt et al. which issued Sept. 6, 1988 discloses grounding the heating element at the forward end of the pointed tip of the nozzle.
A variety of different terminal arrangements are also known in the art. For instance, the applicant's U.S. Pat. Nos. 4,403,405 which issued Sept. 13, 1983 and 4,446,360 (divisional) show a nozzle and method of making it having a terminal protected by a connector sleeve with sealing provided by a split washer assembly. Further developments are shown in the applicant's U.S. Pat. Nos. 4,557,685 and 4,583,284 (divisional) which issued Apr. 22, 1986. More recently, the applicant 's Canadian patent application Ser. No. 549,520 entitled "Method of Manufacture of Injection Molding Nozzle Electrical Terminal" which was filed on Oct. 16, 1987, discloses a method of making a nozzle with a terminal by connecting the rear end of the heating element to a stud and pouring molten insulating material around it. While all of these methods represented considerable improvements at the time, they have the disadvantages that a considerable number of steps are required to make the nozzle and the terminals do not have sufficient structural strength to prevent failure due to torque from the external lead being connected and disconnected.